This application claims the priority of German Application No. 198 27 627.3, filed Jun. 20, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for regulating a supercharged internal combustion engine having two rows of cylinders with an exhaust turbocharger being associated with each row of cylinders, and with a regulating unit in which, taking into account state parameters that describe the operating state of the engine, a control signal is generated to adjust at least one exhaust turbocharger.
A multicylinder internal combustion engine with two parallel exhaust turbochargers is known from U.S. Pat. No. 5,090,204 or German Patent document DE 38 32 965 A1 (which is the patent application from which U.S. Pat. No. 5,090,204 claims priority) . The symmetrically constructed engine consists of two banks of cylinders with an exhaust turbocharger associated with each bank. The turbines are driven by the exhaust in the exhaust line of each cylinder bank. The associated compressor is located in the intake manifold associated with this bank of cylinders.
In order to maintain the boost pressure in the intake manifolds of both cylinders at the same level, a regulating unit is provided that equalizes the differential pressure between the boost pressures in the intake manifolds downstream of the compressors. When a certain deviation occurs, a regulating signal is generated. The regulating signal is used to adjust a throttle located in a bypass line of the respective turbine. As a result, the turbine power, and consequently the compressor performance as well, can be influenced, whereupon an adjusted boost pressure is set in the intake system.
Because of the intrinsic dynamics of the system to be regulated, consisting of turbines, compressors, and throttles, this behavior has the disadvantage that the desired equalization of the boost pressure between the two intake manifolds is established only after a time delay. The regulating intervention at the throttle in the bypass of the turbine initially produces a change in the exhaust counterpressure upstream of the turbine. This change results in a modified turbine power which in turn acts on the boost pressure with a time delay. Particularly during non-steady-state operation of the engine, because of the time-delayed occurrence of the regulatory intervention, an undesired boost pressure differential can be established between the intake manifolds of the two rows of cylinders, so that a non-uniform charging of the cylinders in the two rows of cylinders with combustion air can result.
Another charged internal combustion engine is known from U.S. Pat. No. 4,660,382. Here, the engine is equipped only a single exhaust turbocharger provided with variable turbine geometry for a variable adjustment of the effective turbine cross section. In this device, the boost pressure is measured downstream of the compressor and serves as the basis of the setting of the variable turbine geometry. However, the coordination of the operation of two exhaust turbochargers, one for each row of cylinders, is not the subject of U.S. Pat. No. 4,660,382.
The problem addressed by the invention is to uniformly supply combustion air to a supercharged internal combustion engine having two rows of cylinders with an exhaust turbocharger for each row, especially at all operating points and during non-steady-state operation.
This problem is solved by a method and apparatus according to the present invention. With the method according to the present invention, a state parameter of the engine is measured directly in the compressor or in the vicinity of a compressor, especially a state parameter that is proportional to the air mass flow through the compressor. As a result, a state parameter is established as the basis of regulation that represents measurement of the supply of combustion air to the rows of cylinders. Advantageously, a state parameter is measured in the vicinity of the compressor inlet.
The generated control signal is fed to a control member which directly influences the effective turbine cross section. Advantageously, the turbines of both exhaust turbochargers are provided with variably adjustable turbine geometry. By means of the control member, the effective turbine cross section can be adjusted. A control signal generated in the regulating unit in accordance with the regulating guideline employed is supplied to the control member. Depending on the regulating strategy employed, the state parameter can be regulated by adjusting one or both variable turbine geometries.
The non-steady-state behavior of the engine is particularly improved because deviations in regulation are detected directly and can be compensated more rapidly. The same air mass flow passes through both compressors, and any differences that may result from manufacturing tolerances for example are compensated. This results resulting in improved fuel consumption and low emissions. The regulating section is limited to sizes and engine components that have a direct influence on the air mass flow transmitted.
Differential regulation can be employed as an especially simple and rapidly performed type of regulation. Here, the difference between two variable physical engine state parameters is advantageously measured in the vicinity of the compressor inlet. Preferably, the state parameters include the air mass flow at the compressor inlet, the rpm of the exhaust turbocharger or the diffuser pressure (which is tapped in the inlet area of the compressor diffusers of the turbochargers). The difference between the two exhaust turbochargers is measured from these state parameters, advantageously with the aid of a differential sensor, and used as the basis for regulation. In differential regulation, in an advantageous fashion, the differential value is set to a reference value which is advantageously equal to zero, so that these state parameters assume the same setpoint in the vicinity of both compressor inlets.
According to another regulation method, the state parameter of only one exhaust turbocharger is compared with a set parameter. A differential value is formed from the difference between the state parameters of the first and second exhaust turbochargers. The state parameters of the first exhaust turbocharger and the differential value are added together. At least one of the two state parameters is varied to the point where a differential value assumes a reference value, especially zero. In this design, the exhaust turbocharger, whose state parameter is compared with the setpoint, assumes the task of a lead element. The state parameter of this turbocharger is initially regulated to the setpoint. The other exhaust turbocharger is set to follow the lead exhaust turbocharger, in which the difference between the state parameter of this turbocharger and the state parameter of the lead turbocharger is set to zero, so that the state parameters of both turbochargers assume the same value. The division into a lead and a following turbocharger has the advantage that only the absolute setpoint for the state parameter of the lead turbocharger must be specified, while on the other hand the state parameter of the following turbocharger is adjusted by differential regulation. Such regulation is simple to perform and sturdy from the regulation standpoint.
The setpoint can be added from a compressor characteristic map stored in the regulating unit, said map representing the relationship between the mass throughput and the total pressure ratio at different turbocharger rpm values. In the characteristic map, a plurality of engine operating curves for specific positions of the variable turbine geometry and certain engine rpm values can be stored for various engine loads and engine operating loads such as operation with acceleration or engine braking operation.
It is also possible to provide an exhaust recycling device that includes a recycling line and an adjustable, especially a regulatable, shutoff valve. In this case, state parameters of the exhaust recycling operation can also be stored in the compressor characteristic map.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.